1. Field of the Invention
This invention relates to forestry equipment, and in particular to a feller buncher for felling and accumulating trees.
2. Discussion of the Prior Art
Felling heads are widely used in the logging industry for accumulating in a vertical position several freshly cut trees prior to laying down the bundle at once, to be transported to roadside by a skidder or forwarder. The felling head is mounted to a heavy duty vehicle, such as a drive to tree or swing to tree wheeled or tracked vehicle, for high efficiency logging. Examples of feller buncher and associated felling heads are shown, for example, in U.S. Pat. Nos. 5,813,308; 5,816,299; 6,068,035; 6,173,973; and 6,374,877 which are incorporated by reference for their description of the construction and operation of such devices.
One type of felling head uses a large saw blade disc having peripheral cutting teeth. The disc is rotated in a horizontal plane below a butt plate, with the teeth exposed at the front of the butt plate. As successive trees are cut, harvesting arms are actuated to pull the tree into an accumulation pocket while at the same time an accumulator arm is withdrawn from the accumulation pocket and then moved behind or brought around the bundle of accumulated trees to add the newly cut tree to the bundle. See, for example, the prior art felling head 10 which is illustrated in FIGS. 1-4. Here, an accumulator arm 16, comprising an inner arm 26 pivotally coupled to a frame of the feller 20 at axis 23 and an outer arm 30 pivotally coupled to a distal end of the inner arm 26 at an axis 38, holds cut trees T2-T4 in an accumulation pocket 17. The outer arm 30 is typical of prior art accumulator arms, and has a relatively straight arm configuration for retaining the trees T2-T4 in the pocket 17. Although a straight arm configuration is shown, it is also known in the prior art to provide accumulator arms which curve toward the accumulation pocket 17, so as to interface with the accumulated stems with a concave surface, and present a convex surface to newly cut trees which are being moved into the accumulation pocket.
Referring still to FIGS. 1-4, a cut tree T1, cut by blade 12, is supported on the butt plate 14 and held in place by one or more pivotable harvesting arms 18, which retains the tree T1 against the accumulator arm 16. To add the tree T1 to the existing bundle of trees T2-T4, the hydraulic cylinder 22 is initially activated to enclose the tree T1 between the accumulator arm 16 and the harvesting arm 18 as shown in FIG. 1. To move the tree T1 to the accumulation pocket 17, the hydraulic cylinder 22 is activated to rotate the inner arm 26 outward, as shown in progression in FIGS. 2-4, causing the spring loaded or hydraulically biased outer arm 30 to pivot about the axis 38 (against the bias of the spring or hydraulic cylinder) and to be retracted from the accumulation pocket 17, as seen in FIG. 4. The accumulator arm 16 can then be driven in the opposing direction by the hydraulic cylinder 22 to position the accumulator arm 16 behind the tree T1 to form a bundle of trees T1-T4 in the accumulation pocket 17.
As the arm 16 is driven around the tree T1, the straight arm contacts the tree T1 at a contact point which is offset from a line drawn through the center of the tree, and specifically offset in the direction of the pivot point of the arm. The force applied to the tree by the arm, therefore, has a significant component that tends to drive the tree toward the axis of rotation of the arm, opposite the desired direction that would facilitate withdrawal of the arm part of the tree. Because of this force component, a significant amount of energy is wasted in withdrawing the arm around the tree.
While accumulator arms such as the one shown are generally successful in accumulating trees in an accumulation pocket, as can be seen in FIGS. 1-4, when a new tree is cut and held against the accumulator arm 16, it is difficult for the arm to pull out behind the newly clamped tree T1. Referring particularly to FIGS. 2 and 3, as the outer arm 30 is withdrawn behind the tree, the distance between the edge of outer arm 30 adjacent the tree T1 and the edge of the harvesting arm 18 adjacent T1 decreases as the arm 16 is withdrawn, such that the outer side of the accumulator arm is forced against the cut tree T1 and harvesting arm 18. The arm 16 therefore is pushed against the newly cut tree against the resistive force of the harvesting arm 18, and a significant force and a corresponding expenditure of energy is required to push the harvesting arm 18 over the spring force or hydraulic relief pressure biasing it as the accumulator arm 16 is forced out. This procedure is not only energy intensive, but can also result in damage to the cut tree. Furthermore, when the accumulator arm 16 is configured as shown or with an outer arm curved toward the pocket 17, the outer arm 30 can also become trapped or jammed by a newly cut tree. In this situation, although the inner arm 26 is fully open, the outer arm 30 is unable to withdraw from the bundle. When this occurs, the operator must either try to rearrange the load by jerking the head, or drop the load, both of which are time consuming and hard on the equipment.